A flip chip mounting method is a method in which a bare chip is directly mounted on a substrate, instead of using a packaged IC (Integrated Circuit). Conventionally, as disclosed in Japanese Unexamined Patent Publications No. 11-284022/1999 (Tokukaihei 11-284022, 1999) and No. 11-345302/1999 (Tokukaihei 11-345302, 1999), for example, a bump on a chip and a metal pattern (also referred to as a “land”) on a substrate are connected by pressing the protruding or hemispherical bump against the flat metal pattern from a side opposite to the bump-formed side of the chip.
More specifically, as shown in FIG. 10(a), in order to manufacture a semiconductor device 70, a gold bump 73 is formed on an input/output pad 72 on a bare chip 71 by means of wire bonding or gold plating. Next, the bare chip 71 on which the gold bump 73 is formed is faced down and mounted on a printed wiring substrate 74.
When mounting, a thermo-setting resin 76 is placed on a printed substrate pad 75 patterned on the printed wiring substrate 74, and the bare chip 71 is placed on the printed substrate pad 75, with its surface having the gold bump 73 facing down. Then, heat and pressure are applied from above to the bare chip 71, hardening the thermo-setting resin 76 between the bare chip 71 and the printed wiring substrate 74.
Thus, the printed wiring substrate 74, the thermo-setting resin 6, and the printed substrate pad 75 are connected by the pressure when they are pressed by the bare chip 71 having the gold bump 73, and specifically, in a condition that the printed substrate pad 75 is dented, for example, by a dent depth d.
In the conventional semiconductor device 70, as shown in FIG. 10(b), the area of the gold bump 73 in contact with the printed substrate pad 75 is always smaller than the area of the printed substrate pad 75. That is, in a conventional semiconductor device, the connection is obtained by pressing a small, protruding bump against a large, flat metal pattern.
Also in a conventional semiconductor device, a chip and a substrate may be pressed with heat applied, after a resin is filled in a spacing formed between them, or after a thermo-setting resin film, instead of a resin, is placed between them. Besides, there are no special requirements on the shape of a bump.
However, in the foregoing conventional semiconductor device and the manufacturing method thereof, even if the chip is pressed and fixed to the substrate, the bump just forms a round dent on the metal pattern, and the connection between them is not always satisfactory. Therefore, even if the chip and the substrate are fixed in this state via the thermo-setting resin between them, when another heat application is conducted in a later mounting process, the connection between the bump and the metal pattern might become unsatisfactory under the influence of a stress distortion due to the difference in the thermal expansion coefficient of each material.
For example, in the conventional semiconductor device 70 shown in FIGS. 10(a) and 10(b), when the bare chip 71 is mounted on the printed wiring substrate 74 but not fixed by a fixing jig, etc. and then heat is applied to the printed wiring substrate 74, the hardened thermo-setting resin 76 between the bare chip 71 and the printed wiring substrate 74 is expanded by heat, and the connection between the gold bump 73 on the bare chip 71 and the printed substrate pad 75 on the printed wiring substrate 74 gets easily opened. That is, since only a flat contact resistance between the gold bump 73 and the printed wiring substrate 74 works as a resistance to the thermal expansion of the thermo-setting resin 76, the gold bump 73 and the printed substrate pad 75 get separated, failing to withstand the thermal expansion.
As heat application is completed and the chip is cooled down, the separated gold bump 73 and the printed substrate pad 75 are fixed again, but not at the original position. As a result, the fixing strength of the gold bump 73 and the printed substrate pad 75 here is inferior to the original fixing strength, and the electrical connection tends to become unsatisfactory.
The reason is that, since the thermal expansion coefficient of the thermo-setting resin 76 is large, due to its shrinkage during cooling, the positional relationship between the gold bump 73 and the printed substrate pad 75 relatively deviates both in a vertical direction along the thickness of the chip, and in a horizontal direction along the surface of the chip. As heat application is completed and the chip is cooled down, the thermo-setting resin 76 and the printed substrate pad 75 shrink and the foregoing positional relationship is tried to be restored, but the original positional relationship is not always restored.
Consequently, there is a possibility that the gold bump 73 and the printed substrate pad 75 eventually have a break.